The invention relates to an antenna device for radio telephones.
Radio telephones have an antenna, with the aid of which a wireless connection can be established with corresponding associated transmitter/receiver stations.
Basically there are three possible ways of implementing antennas in a radio telephone.
Firstly, it is possible to use an additional external component as the antenna.
Such an implementation is known for example from the document DE 696 22 451 T2.
The antenna device implemented in accordance with this document comprises an additional antenna component which is brought out from the housing of the radio telephone in question.
Although such an antenna device represents an optimum solution in terms of antenna technology, this solution is however no longer acceptable today in practical terms at least in the mass market for reasons of design.
Secondly, it is possible to use an additional internal component as the antenna.
Such an implementation is known for example from the document DE 102 59 839 A1.
The antenna device implemented in accordance with this document comprises an additional antenna component which can for example be a sheet-metal part or wireframe geometry. In this case, this additional antenna component includes regions which are arranged outside the plane of a carrier used for the antenna arrangement, but also for further electrotechnical precautions. Compared with an arrangement of the antenna device on the same plane as the aforementioned carrier this results in an increased distance between the head of a user of the radio telephone in question and the antenna device of this telephone. In this manner the head of the user is less exposed to the effects of electromagnetic radiation emitted by the telephone. On the other hand, however, the parasitic interference of the radio telephone or its antenna caused by the user is also reduced.
In a side view disclosed in the last-mentioned document said increased distance with respect to the antenna and the strip conductor carrier can be easily seen.
One disadvantage of such an antenna device is the fact that an additional component is used for the antenna, which is expensive to manufacture and complex to assemble.
Thirdly, it is possible to use a printed circuit board antenna or a strip conductor antenna.
Such an implementation is known for example from the document DE 201 12 076 U1.
An antenna device of this type essentially has only one strip conductor as an antenna, which is arranged directly on a strip conductor carrier.
One important disadvantage of this antenna device is the fact that the distance from the strip conductor used as the antenna to an outer wall of the associated radio telephone and thus to the head of a user of said radio telephone is very small. Here too this small distance between radio telephone and head again causes an undesired distortion of the radiation pattern of the antenna device of the telephone in addition to increased exposure of the head of a user of the radio telephone to the electromagnetic radiation emitted by the telephone. As a result, radiation losses due to absorption are again caused which are reflected in a reduced range of the telephone. To compensate for this would mean increasing the radiated power, which in turn results in increased irradiation of high-frequency power into the head of the user.
A loop antenna is known from the document EP 0 986 106 A1, which is arranged with its loop element spaced from the plane of the carrier material carrying the loop antenna by material tensioning of guide elements.
An antenna construction is known from the document WO 2004/066444 A1, which is formed with the aid of a flexible, film-like substrate. On the flexible substrate are placed antenna elements together with both electronics elements and electrical feed lines. The flexible substrate is applied on an upper side of a circuit board and covers the entire upper surface of the latter. In this case it is embodied in such a manner that it projects beyond the upper surface of the circuit board. The part of the flexible substrate, on which the antenna elements are placed, projecting beyond the circuit board is bent back in an arc across the upper surface of the circuit board and forms a second plane at a spacing from the upper surface of the circuit board. The distance between this second plane and the upper surface of the circuit board is fixed by spacers arranged between them.
A similar antenna is disclosed in the document DE 101 24 766 C1, as is known from the document WO 2004/066444 A1.